The present invention relates in general to an automatic weaving loom for producing a woven fabric and particularly to a weft inserting or filling motion to be incorporated into an automatic weaving loom for cyclically shooting or picking a weft yarn into a shed formed between a pair of angularly spaced sets of warp yarns for continuously producing a woven fabric. More specifically, the present invention is concerned with a method of controlling the weft inserting motion of an automatic weaving loom for the purpose of stopping the loom in the event of a failure invited in the loom or, more specifically, in case the weft inserting motion of the loom fails to shoot the weft yarn into the shed of the warp yarns to a length covering the overall width of the shed during operation of the loom. The present invention is further concerned with a control device which is adapted to put such a method into practice in a usual weft inserting motion of an automatic weaving loom.
Failure of picking a weft yarn throughout the width of a shed of warp yarns results in production of defects in a woven fabric and, for this reason, the weft inserting motion incorporated in an automatic weaving loom is usually furnished with a control device which is adapted to detect a shortage of the length of a weft yarn picked into the shed in each of weft inserting cycles and to bring the loom to a stop in the event the weft yarn picked into the shed is short of a predetermined length covering the overall width of the shed of the warp yarns. Such a control device uses mechanical, electrical or, in some cases, an electro-mechanical detecting means responsive to the reach of the pick of a weft yarn to the widthwise foremost end of the shed. None of such detecting means has proved entirely acceptable because they are apt to erroneously respond to the picking motions and thus fail to offer satisfactory reliability of operation. The conventional detecting means may be erroneously actuated to stop the loom even though the weft yarn is picked throughout the width of the shed of the warp yarns and has properly reached the widthwise foremost end of the shed. Or otherwise, the prior art detecting means may happen to fail to detect a pick of the weft yarn which has undershot the end of the shed. If the loom is thus objectionably brought to a stop in the absence of a failure in the weft inserting motion, then production of a stop-mark will result, imparing the commercial value of the fabric produced. If, on the other hand, the loom is permitted to continue the weaving operation with a failure involved in the weft inserting motion by an oversight of the weft yarn short of the prescribed length, the resultant fabric will have critical defects that will also impair the quality of the fabric.
One of the known control devices for use with the weft inserting motions uses an electric circuitry which comprises a first signal generator for producing pulses corresponding to picking cycles and a second pulse generator for producing pulses representative of the picks of the weft yarn shot through the shed of warp yarns to a proper length. The first pulse generator is connected directly and the second pulse generator connected through a logical negation circuit to input terminals of a logical AND gate circuit so that the AND gate circuit produces an output signal in the presence of the pulse from the first pulse generator and concurrently in the absence of the pulse from the second pulse generator, viz., when the weft yarn picked into the shed of the warp yarns is short of a predetermined length and consequently fails to reach the widthwise foremost end of the shed. The loom is temporarily shut down in response to the output signal from the AND gate circuit and is started for a second time when the failure involved in the weft inserting mechanism is removed or remedied.
The prior art control device of this nature is thus operative to detect the weft picking condition in each of the picking cycles of the loom and to stop the loom each time the weft yarn fails to be properly shot into the shed of warp yarns. The output signals delivered from the logical AND gate circuit will therefore contain a signal which is produced by the erroneous actuation of the detecting means. Stopping the loom by such an erroneous actuation of the detecting means will not only result in the formation of a stop-mark in the resultant fabric as previously pointed out but in deterioration of the production efficiency because of the down-time caused by the unnecessary stoppage of the loom. If, however, arrangement is made so that the signals delivered from the control circuitry are monitored with a view to reducing the frequency at which the loom is to be stopped, the quality of the resultant fabric will be improved and at the same time the production efficiency of the loom will be significantly increased. In view of the fact that a fabric is regarded as acceptable on the part of the manufacturer if the fabric contains defects less than a certain number per a certain length of the fabric, the signals delivered from the control circuitry may be monitored in such a manner that the loom is brought to a stop if, and only if, the number of the output signals from the control circuit has exceeded a predetermined number when the fabric is produced a predetermined length. The present invention has been completed on the basis of such a discovery.